How OrbitNight calculates
Every number on OrbitNight is computed from public data with published methods. Here is where each one comes from, how it is worked out and how far you can trust it.
Satellite positions
How it works
Orbits come from Space-Track.org (US Space Command) as two-line element sets (TLEs), fetched about every hour.
Positions are computed with SGP4, the standard model those element sets are made for.
How accurate
Within a few kilometres for a fresh element set, drifting by roughly 1–3 km a day for low orbits. Each satellite page shows how old its element set is. A satellite that has just fired its engines (ISS reboosts, Starlink orbit raising) is off until the next set arrives.
Pass times and “visible to the naked eye”
How it works
A pass runs from when the satellite rises above your horizon to when it sets.
We call it visible when the satellite is in sunlight, the sky where you are is dark (Sun more than 6° below the horizon), and it climbs at least 10° high, above haze and buildings.
Brightness comes from the satellite's standard magnitude, its distance and the angle of sunlight (the formula satellite observers use).
How accurate
Seconds for the next day or two with a fresh element set; a minute or more several days ahead or after a manoeuvre, so check again on the day. Brightness is a typical value, good to about one magnitude: satellites flash and dim as they turn.
Starlink trains
How it works
We take Starlink launches from the last 30 days (Launch Library 2) and find their satellites in the orbit catalogue.
If at least 5 of them are still within 15° of each other along the orbit, the launch counts as a train; its pass times run from the first satellite to the last.
How accurate
Times are as good as for any satellite. Brightness is the uncertain part: trains are brightest in the first days and fade as the satellites climb and turn edge-on.
Aurora chances
How it works
The Kp forecast (3-hour steps, 3 days) comes from NOAA's Space Weather Prediction Center.
Each spot's geomagnetic latitude is worked out from the 2025 IGRF dipole pole. The aurora oval moves about 2.5° toward the equator per Kp step, so a spot needs Kp of about (66° − geomagnetic latitude) ÷ 2.5.
The chance compares the highest Kp forecast during the spot's dark hours (Sun 12° below the horizon) with that need: “good” at one step above, “possible” when it just reaches it, “slim” one step below. Over 85% cloud lowers it to “slim”.
How accurate
A rule of thumb, not a physical model. Kp forecasts beyond a day are often wrong, and short bursts (substorms) can bring the aurora with little warning, so check the live oval on the night.
Cloud cover
How it works
Hourly cloud cover from MET Norway's Locationforecast, at the pass time or averaged over the dark hours.
How accurate
A weather forecast: good for tonight, rougher two or more days ahead, and it cannot see small local clouds.
Moon, planets and sky events
How it works
Computed with Astronomy Engine, an open-source library built on the VSOP87 planetary theory and other published models: rise and set times, Moon phase, planet positions, eclipses and meteor shower peaks.
How accurate
Positions to within about an arcminute; rise and set times to about a minute (the real horizon, hills and refraction add more).
Re-entries
How it works
Space-Track's decay predictions and TIP messages, refreshed hourly as an object comes down.
How accurate
The time stays uncertain by hours until the last day; since an object circles the Earth every 90 minutes, where it falls is not known until the very end.
“What was that light?”
How it works
For the time and part of the sky you give, we list everything that was there: satellites, Starlink trains, rocket bodies, planets, meteor showers and re-entries, ranked by how close each was to the direction you saw and how bright it was.
How accurate
A ranking of likely candidates, not a certainty: the closer your time and direction, the better the match.
What it is not for
OrbitNight is for watching the sky and learning. It is not for navigation, collision avoidance or safety decisions.
Found a mistake? Let us know: orbitnighte@gmail.com